April 15-17

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Author: C C Hegna
Requested Type: Poster
Submitted: 2019-02-21 16:07:45

Co-authors: B. J. Faber, P. W. Terry, I. J. McKinney, A. Bader

Contact Info:
University of Wisconsin-Madison
1500 Engineering Drive
Madison, WI   53706
USA

Abstract Text:
Recent progress in turbulent transport optimization in stellarators is discussed. The goal of this work is to find mechanisms to improve stellarator confinement by optimally using 3D shaping to affect turbulent saturation levels. Predictions for turbulent saturation of ion temperature gradient (ITG) instabilities in stellarator geometry is investigated using a three-field fluid model.
The dominant nonlinear energy transfer process is described coupling of linear instabilities to damped eigenmodes at comparable wave number. The dominant nonlinear energy transfer from unstable to damped modes is enabled by a three-wave interaction, where the identity of the third mode is a function of 3D shaping. The theory identifies an important metric, the product of a turbulent correlation lifetime and a geometric coupling coefficient, which quantifies nonlinear energy transfer. Large values of this metric correspond to small values of ITG-induced turbulent transport. The theory is being extended to accommodate a broader class of micro-instabilities. We discuss possible applications of the theory to trapped electron mode and/or kinetic ballooning mode turbulence in stellarators.

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